How a device adheres to the body should be considered as soon as the designer has a form factor, according to Michael Muchin of Avery Dennison Medical, North America.

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So much work goes into the technology and design of a wearable medical device that sometimes deciding how it will actually be attached to a person can be overlooked until late in the process, said Michael Muchin, business director at Avery Dennison Medical, North America, in an interview with MD+DI.

“Typically, the engineers are focused on the device design and development of the technology that enables the device to work so that bonding to the body can become an afterthought,” he said. “Additionally, in comparison to creating a device, adhering it to the body seems simple.”

But, he said, designing a product to stay on the body is not easy or straightforward. There are many factors that go into choosing the proper adhesive for a specific device, and starting early in the process can be key to ensuring the project stays on their development timeline. What follows are some of the highlights of what Muchin will cover in his session at Boston MEDevice, Navigating Adhesive Obstacles on the Medical Device Design Journey.

Can you give a short overview of what you’ll be talking about at your session at Boston MEDevice?

Muchin: The goal is to provide an overview of what’s involved with keeping a medical device on the body for the required period of time — what that development process looks like, what the pitfalls are, where people have challenges. In general, an overview using the experience that we’ve had in the past.

All of these wearable devices are different. Although we try to use some commonality and knowledge that we have about the products on the market and how developers have been successful in the past, every application is different. I think oftentimes people think, ‘just tell me what I need and we’re on our way,’ and typically it needs to be more collaborative. That’s some of the context we’ll try and weave into this discussion.

It’s about how the adhesive integrates in general in a device, and what the form factor is. Where is it going on the body? How long is it staying on the body? Who is it sticking to? All of those factors play into the success of [a device] meeting the designer’s specification.

Why do you think pressure-sensitive adhesive (PSA) selection is often overlooked when designing a new medical device?

Muchin: I think [designers] spend the majority of their time on the device, on the algorithm, on the form factor for the device, on how the device has to function on the body, that adhering to the body becomes secondary. In my experience, rarely is it a primary concern. Nobody starts by thinking about a medical device and how it will bond to the body. In many instances it’s, ‘I will figure that out later.’

And then, depending on when that ‘later’ is, it can have a major impact on their timeline. Obviously, if the device doesn’t function effectively, then there is no concern about how it bonds to the body. So, there is that balance of working on how the device adheres to the skin once the developer has a functioning device.

But equally, if you wait until you’re all the way developed and you’ve chosen all the materials, you may miss the opportunity to make little nuanced changes in the device design that may not have any impact on how the device functions but could have a major impact on how it bonds to the body.

As an example, if they make a device out of silicone, it’s a more challenging surface to bond to. So, it’s possible to get all the way down the road with this really thin conformable device made of silicone that feels great, but it can limit the adhesive options.

There are those sorts of decisions that get made early in the development process that can impact how well it adheres to the body in the long run.

So, the earlier in the process they are thinking about an adhesive or how it will stick to the body is ideal?

Muchin: And the integration with the device. Yes, correct. Because one plays off the other. If you’re not far enough along in a device design, you can’t really test an adhesive product. And equally, if you start too late, then you’ve already designed the whole device and it could set you back from that perspective.

Why can PSA selection be an obstacle in medical device design?

Muchin: What we were talking about just now was the device itself and the adhesive. What you then bring in are all of the other factors related to who it’s going on. How long does it stay on? What are you doing with it? Is it going underwater? Will the subject be sweating while wearing the device? Are they young or old? Is their skin fragile? All those other factors come into play, which can make it challenging to do.

I equally don’t want to paint a picture that it can’t be done, because obviously it is being done. But the time to market can be delayed, if you don’t figure some of these key design inputs out earlier in the process versus later.

What are some of the steps you would suggest medical device manufacturers take to ensure it’s less of an obstacle?

Muchin: Starting early helps and also testing early. The reality is people don’t understand they’re the best tester. You take something that mimics the size of the device, you bond it to an adhesive patch, and start to wear it for the intended period of time.

The design engineer and their colleagues can become the initial guinea pigs without a real full-blown wear-study data capture. It’s more informal. I think normally when we have customers who do that, it becomes their first real design inputs to say, ‘wait a minute this didn’t work,’ or ‘these people got really upset and the adhesive was too aggressive,’ or vice versa, ‘it fell off the testers after a certain period of time,’ so then you can actually have a real conversation about what it is you’re making and trying to achieve.

And then from there, the evolution starts to happen. ‘Do we need to streamline the device? Or the device isn’t breathable enough. Does the device need channels to help with breathability, is it too heavy and can it be streamlined? Can we make it lighter?’

Put all of those inputs into play and typically you get a view from marketing at that point as well. They may not like the way it looks, or they want to be printed or it needs to be clear, etc.

What are the types of PSAs device manufacturers can consider and are different types more challenging to integrate than others?

Muchin: The vast majority of the products that are on the body are acrylic adhesives, which is a workhorse adhesive. Different sorts of backing material like a nonwoven or a polyurethane nonwoven combination are typical backings that are used with it, with different acrylic adhesives based on how long it is on the body.

Then there are also more specialty adhesives like hydrocolloid. It is a synthetic rubber-based adhesive that has been historically used for ostomy. The adhesive has been used for applications where that product will be on the body for an extended period of time. It does absorb moisture, to a point, and can be a bit gentler on the skin.

Additionally, silicone gel adhesive is gentler than both acrylic and hydrocolloid adhesives. But they often do not have the tack or shear properties needed to hold onto the body for an extended period. People love the gentle feel of the product, but often it will not survive more challenging applications.

Who are the people that you would like to attend your session?

Muchin: I think mainly design engineers — people that are responsible for adhering the device to the body. Typically, they have designed the device as well, so they get the whole project and have intimate knowledge of the device functionality.

And finally, what do you hope attendees will take away from your session?

Muchin: Ultimately, designing a product to adhere to the body is not straightforward and there’s no one-stop-shop answer. And realistically every device is different. We’re leveraging the information we have from past learnings, but equally everything needs to be tested and reviewed.

What worries me about the sector in general is that many people want an immediate answer. They want to input data and come out with an answer and that’s not normally the case. Like we discussed earlier, the device itself is different. Size, weight, who it sticks to, how long it’s on the body, all of those variables are factors that make the product work or not work in the application.

Muchin will present, Navigating Adhesive Obstacles on the Medical Device Design Journey, on Thursday, September 26, at 11:15 am to 12:00 pm EST, on the Center Stage.

article source: MDDI